Method and device for device to device communication

ABSTRACT

The present disclosure relates to a 5G or pre-5G communication system for supporting a higher data transmission rate than a 4G communication system such as LTE. The method for device to device communication according to the present disclosure comprises: a step of receiving, by a terminal, search data from search resources for relay search within a specified search-receiving resource pool, and decoding the same; a step of measuring, by the terminal, link qualities of the search resources which deliver demodulation reference signals, from the search resources corresponding to successfully decoded search data; and a step of filtering a link quality corresponding to an identifier of a specific relay among the measured link qualities.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/505,912,which is the National Stage of International Application No.PCT/KR2016/006216, filed Jun. 10, 2016, which claim priority to IndianApplication No. 645/KOL/2015, filed Jun. 10, 2015, and IndianApplication No. 1007/KOL/2015, filed Sep. 23, 2015, each of which areincorporated herein by reference into the present disclosure as if fullyset forth herein.

BACKGROUND 1. Field

The present disclosure relates to a method and an apparatus forsearching for and discovering a relay in a communication systemsupporting device to device direct communication.

2. Description of Related Art

In order to meet wireless data traffic demands that have increased after4th Generation (4G) communication system commercialization, efforts todevelop an improved 5G communication system or a pre-5G communicationsystem have been made. For this reason, the 5G communication system orthe pre-5G communication system is called a beyond 4G networkcommunication system or a post LTE system.

In order to achieve a high data transmission rate, an implementation ofthe 5G communication system in a mmWave band (for example, 60 GHz band)is being considered. In the 5G communication system, technologies suchas beamforming, massive MIMO, Full Dimensional MIMO (FD-MIMO), an arrayantenna, analog beam-forming, and a large scale antenna are discussed tomitigate a propagation path loss in the mmWave band and increase apropagation transmission distance.

Further, technologies such as an evolved small cell, an advanced smallcell, a cloud Radio Access Network (cloud RAN), an ultra-dense network,Device to Device communication (D2D), a wireless backhaul, a movingnetwork, cooperative communication, Coordinated Multi-Points (COMP), andinterference cancellation have been developed to improve the systemnetwork in the 5G communication system.

In addition, the 5G system has developed Advanced. Coding Modulation(ACM) schemes such as Hybrid FSK and CLAM Modulation (FOAM) and SlidingWindow Superposition Coding (SWSC), and advanced access technologiessuch as Filter Bank Multi Carrier (FBMC), Non Orthogonal Multiple Access(NOMA), and Sparse Code Multiple Access (SCMA)

Meanwhile,due to the recent emergence of the Internet of Things,interest in a D2D communication technology which is one of thecommunication methods for interworking with a smart device hasincreased. The D2D communication technology operates based on physicalproximity between User Equipments (UEs) and has many advantages in termsof an increase in efficiency of network resources, a decrease in UEpower consumption, and an expansion of a cellular communication area. Inorder to reflect such a situation, a D2D technology was selected as astudy item, and feasibility research of a Proximity-based Service(ProSe) was started in Release 12 through 3GPP in 2011 and earneststandardization work was started in 2013.

A D2D UE, which is a transmitter, may transmit data packets to a UEgroup including intended D2D UEs or broadcast data packets to all D2DUEs during communication. D2D communication between the transmitter andreceiver(s) essentially corresponds to a non-connection. That is, beforethe transmitter starts transmission of data packets, there is noconnection configuration between the transmitter and the receiver.Further, when transmitting data packets, the transmitter inserts asource ID and a destination ID into the data packets. The source ID isset as a LIE ID of the transmitter. The destination ID corresponds to abroadcast ID or a group ID of the receiver to receive the transmittedpacket.

One of the D2D communication requirements is to make an out-of-coverageremote UE communication with a network through another UE that is withinthe network coverage and is close to the remote UE. As described above,a UE that serves as a relay is referred to as a “relay UE”.

FIG. 1 illustrates an example in which a remote UE communicates with arelay UE through D2D communication.

Referring to FIG, 1, a remote UE 101 may communicate with a networkthrough a UE-to-Network relay 102 (hereinafter, referred to as a relayUE) and corresponds to a UE which desires to communicate with thenetwork through the relay UE and is within the network coverage. D2Dcommunication 104 is performed between the remote UE 101 and the relayUE 102, and cellular communication 105 is performed between the relay UE102. and an eNB 103.

A D2D direct discovery process is used for discovering the relay LTE, Inorder to make the remote UE 101 discover the relay UE 102, the relay UE102 may periodically transmit (or announce) discovery information (forexample, a UE ID and a notification indicating that the UE IDcorresponds to the relay UE) through a relay discovery announcementmessage and, accordingly, the remote UE may use the relay discoveryannouncement message to search for/discover a nearby relay UE. Theremote UE monitors discovery resources or a physical channel fordiscovery information transmitted by neighboring UEs to discover thenearby relay UE.

in communication between devices used by the relay UE to expand thecoverage, the remote UE may find a plurality of UEs to act as a relaybetween the network and the remote UE, and should select a best UE ofthe found UEs as the relay UE. Further, even when the remote UEre-selects another relay UE, the same operations are performed duringcommunication with the relay UE. In the relay UE selection andre-selection, the most important information for the selection is linkquality for a link (that is, a D2D link) between the remote UE and relayUE candidates.

100141 There are two methods to measure the D2D link quality. In thefirst method, the D2D link quality is measured using reference signals(RSs) transmitted to physical resource blocks (PRBs) of a physicalsidelink broadcast channel (PSBCH). In the second method, the D2D linkquality is measured using reference signals transmitted to PRBs of aphysical sidelink discovery channel (PSDCH).

SUMMARY

In the first method, since PSBCHs transmitted by the relay UE candidatesare all the same, link quality between the remote UE and each of therelay UE candidates should be identified and measured to select therelay UE. Accordingly, such a method cannot be used for measuring theD2D link quality. Further, a protocol stack for transmission/receptionof a discovery message in a currentsystem includes a radio resourcecontrol (RRC) layer, a physical (PHY) layer, a media access control(MAC) layer, and a proximity service (ProSe) protocol. To measure thelink quality, the radio resource control (RRC) layer configuresmeasurement for the physical (PHY) layer, and the PHY layer performs themeasurement and provides a result of the measurement to the RRC layer.However, in the measurement of the D2D link quality, an ID of the relayHE is not known to the P layer. This is because, the discovery messagepenetrates the PHY layer. Further, unique discovery resources for aparticular relay UE are also not known. Accordingly, to discover the D2Dlink, the remote UE should monitor all the configured discoveryresources and the PHY layer cannot measure the particular relay UE andcannot provide a measurement value to the RRC layer. Therefore, thesecond method is also not suitable for the D2D link quality.

Accordingly, the present disclosure provides a method of measuring aparticular relay UE and determining the measurement, and an apparatusfor the same.

According to an embodiment of the present disclosure, a method of deviceto device direct communication includes: receiving and decodingdiscovery data in discovery resources for discovering a relay within apredetermined discovery reception resource pool by a UE; measuring linkqualities for discovery resources carrying demodulation referencesignals in discovery resources corresponding to successfully decodeddiscovery data by the UE; and filtering a link quality corresponding toan ID of a predetermined relay among the measured link qualities.

According to another embodiment of the present disclosure, a UEapparatus for device to device direct communication includes: atransceiver that performs cellular communication with a BS and performsdevice to device direction communication with a counterpart UE through adirect communication path; and a controller that receives and decodesdiscovery data in discovery resources for discovering a relay within apredetermined discovery reception resource pool, measures link qualitiesfor discovery resources carrying demodulation reference signals indiscovery resources corresponding to successfully decoded discoverydata, and filters a link quality corresponding to an ID of apredetermined relay among the measured link qualities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an examplein which a remote UE communicates with arelay UE through D2D comms nication;

FIGS. 2 and 3 illustrate a D2D link quality measurement method for arelay according to a first embodiment of the present disclosure;

FIG. 4 illustrates a D2D link quality measurement method for a relayaccording to a second embodiment of the present disclosure;

FIG. 5 illustrates a configuration of a discovery MAC PDU according toan embodiment of the present disclosure;

FIG. 6 illustrates a method of measuring D2D link qualities fordifferent UEs according to a third embodiment of the present disclosure;

FIG. 7 illustrates a method of measuring D2D link qualities fordifferent UEs according to a fourth embodiment of the presentdisclosure;

FIG. 8 illustrates a method of measuring D2D link qualities fordifferent UEs according to a fifth embodiment of the present disclosure;

FIG. 9 illustrates a method of measuring D2D link qualities fordifferent UEs according to a sixth embodiment of the present disclosure;

FIG. 10 illustrates a method of measuring D2D link qualities fordifferent UEs according to a seventh embodiment of the presentdisclosure;

FIGS. 11 and 12 schematically illustrate a method of measuring a D2Dlink quality for a UE according to an embodiment of the presentdisclosure;

FIG. 13 illustrates an example of measurement according to easuremewindow; and

FIG. 14 illustrates a configuration of an apparatus of a UE according toan embodiment of the present disclosure.

DETAILED DESCRRIPTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In the followingdescription of the present disclosure, a detailed description of knownconfigurations or functions incorporated herein will be omitted when itis determined that the detailed description may make the subject matterof the present disclosure unclear. The terms as described below aredefined in consideration of the functions in the embodiments, and themeaning of the terms may vary according to the intention of a user oroperator, convention., or the like. Therefore, the terms should bedefined on the basis of the contents throughout the specification.

In the detailed description of the present disclosure, an example ofinterpretable meanings of some terms used in the present disclosure isproposed. However, it is noted that the terms are not limited to theexamples of the construable meanings which are proposed below.

A base station is a subject communicating with a User Equipment (UE),and may be referred to as a BS, a Node B (NB), an eNode B (eNB), anAccess Point (AP) or the like. The user equipment is a subjectcommunicating with the BS, and may be referred to as a UE, a MobileStation (MS), a;Mobile Equipment (ME), a device, a terminal or the like

Hereinafter, D2D link quality measuring methods for different UEsaccording to an embodiment of the present disclosure will be describedwith reference to the drawings. The link quality measuring methodsdescribed below may be performed by the remote UE and/or the relay UE.

FIG. 2 illustrates D2D link quality measuring methods for different UEsaccording to a first embodiment of the present disclosure.

Referring to FIG. 2, a layer measures link quality on each discoveryresource (or PRBs) or discovery resources (or PRBs) by which discoveryprotocol data units (PDUs) are successfully received (that is,successfully decoded or passing through a cyclic redundancy check(CRC)), that is, reference signal received power (RSRP), referencesignal received quality (RSRQ), or received signal strength indicator(RSSI) according to an instruction 201 of an RRC layer in step 202. Atthis time, measurement values for PRBs on which the successfullyreceived discovery PDUs are repeated are measured. In each of thesuccessfully received discovery PDUs, measurement values correspondingto all transmissions for the discovery PDUs including the repetition arecombined(averaged) into one or each of the measurement values isassociated with the corresponding discovery PDU. The measurement may beperformed on demodulation reference signals (DMRSs) transmitted throughdiscovery PRBs.

Discovery resources measured by the PHY layer may be one of thefollowing discovery resources.

First, discovery resources within all discovery reception (RX) resourcepools

Second, discovery resources within all public safety (PS) discovery RXresource pools

Third, discovery resources within all relay UE discovery RX resourcepools

Further, the PHY layer decodes discovery PHY PDUs through the discoveryresources. The PHY layer transmits a measurement result for thediscovery resources of the discovery PHY PDUs having been successfullydecoded (having passed through the CRC) to a MAC layer in step 203. Atthis time, measurement values for PRBs on which the successfullyreceived discovery PDUs are repeated are measured. In each of thesuccessfully received discovery PDUs, measurement values correspondingto all transmissions for the discovery PDUs including the repetition arecombined (averaged) into one, or each of the measurement values iscombined with the corresponding discovery PDU and transmitted to the MAClayer. The measurement result is transmitted along with decodeddiscovery MAC PDUs (PRY PDUs having not passed through the CRC).

The MAC layer transmits the discovery message and the measurement resultreceived from the PHY layer to a ProSe protocol in step 204. At thistime, according to an embodiment, the measurement result may not bedirectly transmitted to the ProSe protocol. In this case, a measureddiscovery MAC PDU list may be stored in an access stratum (AS) (MAC orRRC) layer, and an order of the measured list may be the same as anorder of the transmitted discovery message. Further, each discoverymessage transmitted to the ProSe protocol may be indexed within the ASlayer. According to another embodiment, among the discovery messages,only a discovery message having a signal strength higher than a set (orpreset) threshold may be transmitted to the ProSe protocol.

The ProSe protocol determines whether the discovery message is a relayUE discovery message (an announcement, request, or response message)based on fields within the received discovery message in step 205. Whenthe discovery message is the relay UE discovery message, the ProSeprotocol transmits a relay ID and the measurement result receivedthrough the discovery message to the RRC layer in step 206. When thediscovery message is not the relay UE discovery message, the ProSeprotocol does not transmit the corresponding message to the RRC layer.When transmitting the relay ID and the measurement result to the RRClayer, the ProSe protocol may also transmit other measurement-relatedinformation received through the discovery message to the RRC layer.Further, according to an embodiment, the ProSe protocol may identifywhether the UE having performed the measurement is interested in thecorresponding relay based on higher layer parameters. The ProSe protocolay transmit the relay ID and the measurement result received through thediscovery message to the RRC layer only when the UE is interested in thecorresponding relay, and, otherwise, does not transmit them.

FIG. 3 illustrates an embodiment of not ansmitting the measurementresult to the ProSe protocol in the method of measuring the D2D linkqualities for different UE according to the first embodiment of thepresent disclosure.

Referring to FIG. 3, steps 301 to 303 are the same as steps 201 to 203of FIG. 2. The MAC layer having received the decoded discovery MAC PDUsand the measurement result from the PRY layersmits the discovery messageto the ProSe protocol and, at this time, also transmits an index of thediscovery message instead of the measurement result in step 304.Further, the MAC layer transmits the measurement result and the index tothe RRC layer in step 305. The RRC layer may maintain the measurementlist and identify each discovery message or the measurement of the relayUE corresponding to the discovery message based on the received index instep 306.

Meanwhile, the ProSe protocol determines whether the discovery messagereceived from the MAC layer is a relay UE discovery message (anannouncement, request, or response message) based on fields within thereceived discovery message in step 307. When the discovery message isthe relay UE discovery message, the ProSe protocol transmits the relayID and the index received through the discovery message to the RRC layerin step 308. When the discovery message is not the relay UE discoverymessage, the ProSe protocol does not transmit the corresponding messageto the RRC layer. For example, when 5 messages are transmitted to theProSe protocol the messages have numbers from 1 to 5. Measurement valueswithin the measurement list corresponding to the message also havenumbers from 1 to 5. Accordingly, when the relay identified by the ProSeprotocol corresponds to message 5, the ProSe protocol transmits index 5to the RRC layer.

The RRC layer may identify the measurement value from the measurementlist maintained within the RRC layer based on the index received fromthe ProSe protocol. Further, the RRC layer uses information receivedfrom the ProSe protocol to select/re-select a relay. That is, in orderto avoid a sudden wireless change of relay UEs in a final candidatelist, a moving average, that is, signal strength filtering is performed.Then, the relay UEs in the final candidate list are ranked in adescending order of a signal strength and a best relay UE (having thehighest signal strength) is selected. According to an embodiment, theranking may be performed only when two or more relay UEs exist.According to an embodiment, the ranking may be performed only for relayUEs having the signal strength higher than a threshold value.

According to an embodiment, the ProSe protocol may select/re-select arelay UE by using the measurement result without transmitting themeasurement result to the RRC layer. That is, in order to avoid a suddenwireless change of relay UEs in the final candidate list, the movingaverage, that is, signal strength filtering is performed. Then, therelay UEs in the final candidate list are ranked in a descending orderof a signal strength and a best relay UE (having the highest signalstrength) is selected. According to an embodiment, the ranking may beperformed only when two or more relay UEs exist. Further, according toan embodiment, the ranking may be performed only for relay UEs havingthe signal strength higher than a threshold value. In addition,according to an embodiment, the ProSe Protocol may select/re-select therelay UE by transmitting the measurement result to the MAC layer.Moreover, according to an embodiment, the measurement instruction may betransmitted to the PHY layer instead of the RRC layer by a higher layer(the ProSe protocol or the MAC layer)

FIG. 4 illustrates a method of measuring D2D link qualities fordifferent UEs according to a second embodiment of the presentdisclosure.

Referring to FIG. 4, a layer measures link quality on each discoveryresource (or PRBs) or discovery resources (or PRBs) by which discoveryprotocol data units (PDUs) are successfully received (that is,successfully decoded or passing through a cyclic redundancy check(CRC)), that is, reference signal received power (RSRP), referencesignal received quality (RSRQ), or received signal strength indicator(RSSI) according to an instruction 401 of an RRC layer in step 402. Atthis time, measurement values for PRBs on which the successfullyreceived discovery PDUs are repeated are measured. In each of thesuccessfully received discovery PDUs, measurement values correspondingto all transmissions for the discovery PDUs including the repetition arecombined (averaged) into one, or each of the measurement values isassociated with the corresponding discovery PDU. The measurement may beperformed on demodulation reference signals (DMRSs) transmitted throughdiscovery PRBs.

Discovery resources measured by the PHY layer may be one of thefollowing discovery resources.

First, discovery resources within all discovery reception (RX) resourcepool

Second, discovery resources within all public safety (PS) discovery RXresource pools

Third, discovery resources within all relay UE discovery RX resourcepools

Further, the PHY layer decodes discovery PHY PDUs through the discoveryresources. The PHY layer transmits a measurement result for thediscovery resources of the discovery PHY PDUs having been successfullydecoded (having passed through the CRC) to a MAC layer in step 403. Atthis time, measurement values for PRBs on which the successfullyreceived discovery PDUs are repeated are measured. In each of thesuccessfully received discovery PDUs, measurement values correspondingto all transmissions for the discovery PDUs including the repetition arecombined (averaged) into one, or each of the measurement values iscombined with the corresponding discovery PDU and transmitted to the MAClayer. The measurement result is transmitted along with decodeddiscovery MAC PDUs (PHY PDUs having not passed through the CRC).

The MAC layer transmits the discovery message received from the PHYlayer to a ProSe protocol in step 404.

Further, based on fields within the discovery message received from thePHY layer, the MAC layer determines whether the discovery message is arelay UE discovery message (an announcement, request, or responsemessage) in step 405. When the discovery message is the relay UEdiscovery message, the MAC layer transmits a relay ID and themeasurement result received through the discovery message to the RRClayer in step 406. When the discovery message is not the relay UEdiscovery message, the MAC layer ignores the corresponding messagewithout transmitting the corresponding message to the RRC layer.

According to an embodiment, the discovery message may be a discoverymessage related to the measurement, which is transmitted by the relayUE. When receiving the discovery MAC MU, the MAC layer checks whetherthere is the discovery message. When the discovery message exists in thediscovery MAC PDU, the MAC layer informs the RRC layer of themeasurement result and other information received through the discoverymessage. When the discovery message does not exist in the discovery MACMU, the MAC layer transmits the discovery message to the ProSe protocol.The RRC layer uses information received from the MAC layer toselect/re-select a relay. That is, in order to avoid a sudden wirelesschange of relay UEs in a final candidate list, a moving average, thatis, signal strength filtering is performed. Then, the relay UEs in thefinal candidate list are ranked in a descending order of a signalstrength and a best relay UE (having the highest signal strength) isselected. According to an embodiment, the ranking may be performed onlywhen two or more relay UEs exist. Further, according to an embodiment,the ranking may be performed only for relay UEs having the signalstrength higher than a threshold value.

According to another embodiment, the MAC layer may select/re-select arelay UE by using the measurement result without transmitting themeasurement result to the RRC layer. That is, in order to avoid a suddenwireless change of relay UEs in a final candidate list, a movingaverage, that is, signal strength filtering is performed. Then, therelay UEs in the final candidate list are ranked in a descending orderof a signal strength and a best relay UE (having the highest signalstrength) is selected. According to an embodiment, the ranking may beperformed only when two or more relay UEs exist. Further, according toan embodiment, the ranking may he performed only for relay UEs havingthe signal strength higher than a threshold value.

Further, according to an embodiment, the measurement instruction may betransmitted to the PHY layer instead of the RRC layer by a higher layer(the ProSe protocol or the MAC layer)

In addition, according to the second embodiment of the presentdisclosure, a protocol stack for transmission of the discovery messagemay be changed.

According to an embodiment, the MAC layer may be non-permeable and,accordingly, fields related to the relay UE measurement are added to aMAC header. This is illustrated in FIG. 5.

According to another embodiment, the PHY may be non-permeable and,accordingly, an L2ID is added to a CRC mask or a PHY header. Theidentification of the relay UE discovery message is based on eachresource pool for the relay, or the ID is included in a CRC mask or aPHY header.

According to another embodiment, both the PHY and the MAC may benon-permeable accordingly, some information may be included in the MACand some information may be included in the PHY.

According to another embodiment, the protocol stack for discoverymessage transmission is not changed, but the MAC layer of the receivermay acquire L2ID and/or other measurement-related information byanalyzing some fields of the discovery message.

FIG. 6 illustrates a method of measuring D2D link qualities fordifferent UEs according to a third embodiment of the present disclosure.

Referring to FIG. 6, a PHY layer decodes discovery PHY PDUs throughdiscovery resources and transmits discovery resource information to aMAC layer along with the decoded discovery MAC PDUs (PHY PDUs withoutCRC) in step 601.

The PHY layer transmits information on the discovery resources on whichthe discovery PDUs have been successfully decoded for one of thefollowing discovery resources to the MAC layer.

First, discovery PHY PDUs received on discovery resources within alldiscovery RX resource pools

Second, discovery PHY PDUs received on discovery resources within all PSdiscovery RX resource pools

Third, discovery PHY PDUs received on discovery resources within allrelay UE discovery RX resource pools

The MAC layer transmits the discovery message and the discovery resourceinformation received from the PHY layer to a ProSe protocol in step 602.

Based on fields within the discovery message received from the MAClayer, the ProSe protocol determines whether the received discoverymessage is a relay UE discovery message (an announcement, request, orresponse message) in step 603. The ProSe protocol transmits a relay IDand discovery resource information received through the discoverymessage to the RRC layer in step 604 when the discovery message is therelay LIE discovery message, and ignores the discovery information whenthe discovery message is not the relay UE discovery message. At thistime, other measurement-related information received through thediscovery message is also transmitted to the RRC layer. Further, theProSe protocol may identify whether the UE is interested in thecorresponding relay based on higher layer parameters. The ProSe protocolmay transmit the relay ID and the discovery resource informationreceived through the discovery message to the RRC layer only when the UEis interested in the corresponding relay, and, otherwise, may ignore therelay ID and the discovery resource information without transmittingthem.

The RRC layer instructs the PHY layer to measure the PSDCH in step 605.At this time, the RRC layer provides the discovery resource informationreceived from the ProSe protocol to the PHY layer.

The PHY layer performs the measurement based on the discovery resourceinformation received from the RRC layer in step 606, and provides aresult of the measurement to the RRC layer or the MAC layer in step 607.When the PHY layer provides the result of the measurement to the MAClayer, the MAC layer may transmit the result of the measurement to theRRC layer or select/re-select the relay based on the result of themeasurement. In a method of measuring the discovery resource informationby the PHY layer, the PHY may measure the discovery resource information(that is, PRBs) instructed by the RRC layer at every discovery period ordetermine PRBs within the next discovery period based on a predeterminedpattern and measure the determined PRBs. At this time, the PRBsinstructed by the RRC may be for the previous period.

According to an embodiment, the ProSe protocol may transmit the relay UEID and the discovery resource information received through the discoverymessage to the MAC layer. Then, the MAC layer instructs the PHY layer toperform measurement, the PHY layer ay transmit a result of themeasurement to the MAC layer, and the MAC layer may performselection/re-selection based on the received result of the measurementor transmit the result to the RRC layer.

FIG. 7 illustrates a method of measuring D2D link qualities fordifferent UEs according to a fourth embodiment of the presentdisclosure.

Referring to FIG. 7, a PHY layer decodes discovery PHY PDUs throughdiscovery resources and transmits discovery resource information to aMAC layer along with the decoded discovery MAC PDUs (PHY PDUs withoutCRC) in step 701.

The PHY layer transmits information on the discovery resources on whichdiscovery PHY PDUs have been successfully decoded for one of thefollowing discovery resources to the MAC layer.

First, discovery PHY PDUs received on discovery resources within alldiscovery RX resource pools

Second, discovery PHY PDUs received on discovery resources within all PSdiscovery RX resource pools

Third, discovery PRY PDUs received on discovery resources within allrelay UE discovery RX resource pools

The MAC layer transmits the discovery message received from the PHYlayer to a ProSe protocol in step 702, Further, the MAC layer determineswhether the received discovery message is a relay UE message (anannouncement, request, or response message) based on fields within thereceived discovery message in step 703. The ProSe protocol transmits arelay ID and discovery resource information received through thediscovery message to the RRC layer in step 704 when the discoverymessage is the relay UE discovery message, and ignores the discoverymessage when the discovery message is not the relay UE discoverymessage. At this time, other measurement-related information receivedthrough the discovery message is also transmitted to the RRC layer.

According to an embodiment, the discovery message may be ameasurement-related discovery message, and the discovery message istransmitted by the relay UE. When receiving the discovery MAC PDU, theMAC layer checks whether there is the discovery message. The MAC layerinforms the RRC layer of a measurement result and other informationreceived through the discovery message when the discovery messageexists, and transmits the discovery message to the ProSe protocol whenthe discovery message does not exist.

The RRC layer instructs the PHY layer to measure the PSDCH in step 705.At this time, the RRC layer provides the discovery resource informationreceived from the ProSe protocol to the PHY layer.

The PHY layer performs the measurement based on the discovery resourceinformation received from the RRC layer in step 706, and provides aresult of the measurement to the RRC layer or the MAC layer in step 707.In a method of measuring the discovery resource information by the PHYlayer, the PHY may measure the discovery resource information (that is,PRBs) instructed by the RRC layer at every discovery period or determinePRBs within the next discovery period based on a predetermined patternand measure the determined PRBs. At this time, the PRBs instructed bythe RRC may be for the previous period.

According to an embodiment, the MAC layer may directly transmit themeasurement instruction directly to the PHY layer instead oftransmitting the measurement instruction to the PHY via the RRC layer.Then, after performing the measurement according to the measurementinstruction, the PHY layer may transmit the measurement result to theMAC layer and the MAC layer may perform selection/re-selection based onthe measurement result or transmit the result to the RRC layer.

Further, according to the fourth embodiment of the present disclosure,the protocol stack for discovery message transmission may be changed,which is the same as the description in the second embodiment.

FIG. 8 illustrates a method of measuring D2D link qualities fordifferent UEs according to a fifth embodiment of the present disclosure.

Referring to FIG. 8, a PHY layer decodes discovery PHY PDUs throughdiscovery resources and transmits the decoded discovery MAC PDUs (PHYPDUs without CRC) to an MAC layer in step 801. The MAC layer transmitsthe discovery message received from the PHY layer to a ProSe protocol instep 802.

The ProSe protocol determines whether the discovery message receivedfrom the MAC layer is a relay UE discovery message (an announcement,request, or response message) in step 803. The ProSe protocol transmitsa relay ID received through the discovery message and discovery resourceinformation included in the discovery message to the RRC layer in step804 when the discovery message is the relay UE discovery message, andignores the discovery information when the discovery message is not therelay UE discovery message. At this time, other measurement-relatedinformation received through the discovery message is also transmittedto the RRC layer. Further, the ProSe protocol may identify whether theUE is interested in the corresponding relay based on higher layerparameters. The ProSe protocol may transmit the relay ID and thediscovery resource information received through the discovery message tothe RRC layer only when the UE is interested in the corresponding relay,and, otherwise, may ignore the relay ID and the discovery resourceinformation without transmitting them.

The RRC layer instructs the PHY layer to measure the PSDCH in step 805.At this time, the RRC layer provides the discovery resource informationreceived from the ProSe protocol to the PHY layer.

The PHY layer performs the measurement based on the discovery resourceinformation received from the RRC layer in step 806, and provides aresult of the measurement to the RRC layer or the MAC layer in step 807.In a method of measuring the discovery resource information by the PHYlayer, the PHY may measure the discovery resource information (that is,PRBs) instructed by the RRC layer at every discovery period or determinePRBs within the next discovery period based on a predetermined patternand measure the determined PRBs. At this time, the PRBs instructed bythe RRC may be for the previous period. Further, the PRBs may correspondto only the next discovery period.

FIG. 9 illustrates a method of measuring D2D link qualities fordifferent UEs according to a sixth embodiment of the present disclosure.

Referring to FIG. 9, a PHY layer decodes discovery PHY PDUs throughdiscovery resources and transmits the decoded discovery MAC PDUs to anMAC layer in step 901. The MAC layer determines whether the receiveddiscovery message is a relay UE discovery message (an announcement,request, or response message) in step 903. The MAC layer transmits arelay ID received through the discovery message and discovery resourceinformation included in the discovery message to the :RRC layer in step904 when the discovery message is the relay UE discovery message, andignores the discovery message when the discovery message is not therelay UE discovery message. At this time, other measurement-relatedinformation received through the discovery message is also transmittedto the RRC layer.

According to an embodiment, the discovery message may be ameasurement-related discovery message, and the discovery message istransmitted by the relay UE, receiving the discovery MAC PDU, the MAClayer checks whether there is the discovery message. The MAC layerinforms the RRC layer of a measurement result and other informationreceived through the discovery message when the discovery messageexists, and transmits the discovery message to the ProSe protocol whenthe discovery message does not exist.

The RRC layer instructs the PHY layer to measure the PSDCH in step 905.At this time, the RRC layer provides the discovery resource informationreceived from the ProSe protocol to the PHY layer.

The PHY layer performs the measurement based on the discovery resourceinformation received from the RRC layer in step 906, and provides aresult of the measurement to the RRC layer or the MAC layer in step 907.In a method of measuring the discovery resource information by the PHYlayer, the PHY may measure the discovery resource information (that is,PRBs) instructed by the RRC layer at every discovery period or determinePRBs within the next discovery period based on a predetermined patternand measure the determined PRBs. At this time, the PRBs instructed bythe RRC may be for the previous period. Further, the PRBs may correspondto only the next discovery period.

According to an embodiment, the ProSe protocol may transmit the relay UEID and the discovery resource information received through the discoverymessage to the MAC layer. Then, the MAC layer may instruct the PHY layerto perform the measurement, and the MAC layer may perform themeasurement and transmit a result of the measurement to the MAC layer.Thereafter, the MAC layer may perform selection/re-selection based onthe measurement result or transmit the result to the RRC layer.

Further, according to the sixth embodiment of the present disclosure,the protocol stack for discovery message transmission may be changed,which is the same as the description in the second embodiment,

FIG. 10 illustrates a method of measuring D2D link qualities fordifferent UEs according to a seventh embodiment of the presentdisclosure.

According to the seventh embodiment of the present disclosure, the PSSCHis used for measuring the link quality instead of using the PSDCH. Usingthe PSSCH to measure the link quality involves passing through the wholelayer 2 stack. Data resources by which data is scheduled (instructed byan SA) are known to receiver nodes. The SA involves an L1 ID ofinterest.

Referring to FIG. 10, the RRC layer provides a PSSCH measurementinstruction to the PHY layer in step 1001, and the PHY layer measuresRSRP or RSRQ for each PSSCH resource by which the data instructed by theSA is scheduled in step 1002. Further, the PHY layer transmits theRSRP/RSRQ measured for the data resources corresponding to thesuccessfully decoded data PDUs to the MAC layer along with the decodedMAC PDUs in step 1003. The MAC layer decodes the received MAC PDUs to beRLC PDUs and transmits the decoded RLC PDUs to an RLC layer along withthe measured RSRP/RSRQ in step 1004. The RLC layer decodes the receivedRLC PDUs to he PDCP PDUs and transmits the decoded PDCP PDUs to a PDCPlayer along with the measured RSRP/RSRQ in step 1005. The PDCP layerdecodes the received PDCP PDUs to be the discovery message and transmitsthe decoded discovery message and the RSRP/RSRQ value to a ProSeprotocol in step 1006. The ProSe protocol determines whether thereceived discovery message is a relay UE discovery message (anannouncement, request, or response message) in step 1007. The ProSeprotocol transmits a relay ID and the measured RSRP/RSRQ receivedthrough the discovery message to the RRC layer in step 1008 when thediscovery message is the relay UE discovery message, and does nottransmit the corresponding message to the RRC layer when the discoverymessage is not the relay UE discovery message. When transmitting therelay identifier and the measurement result to the RRC layer, the ProSeprotocol may also transmit other measurement-related informationreceived through the discovery message to the RRC layer. Further,according to an embodiment, the ProSe protocol may identify whether theUE having performed the measurement is interested in the correspondingrelay based on higher layer parameters. The ProSe protocol may transmitthe relay identifier and the measurement result received through thediscovery message to the RRC layer only when the UE is interested in thecorresponding relay, and, otherwise, does not transmit them.

In the aforementioned first to seventh embodiments of the presentdisclosure, the data resources instructed by the SA may be used insteadof the discovery resources.

Meanwhile, in the current system,when the remaining D2D grant(s) validfor a scheduling control (SC) period can accept all pending data (in abuffer) which can be used for transmission, all triggered D2D bufferstate reports (BSR) should be cancelled. A procedure of cancelling theD2D BSRs considers future data transmissions to which the grants areallocated but which have not yet happened. According to such a scheme,when some data reaches the buffer before the last transmission withinthe SC period, the buffer state is not empty at the moment when the datareaches the buffer, so that the D2D BSRs are not triggered until are-transmission timer expires, which delays the D2D BSR triggering.

Accordingly, in order to overcome the problems, the present disclosureproposes the following D2D BSR triggering method.

When there is no pending data which can be used for transmission, alltriggered D2D BSRs should be cancelled. At this time, grants for futuretransmission are not considered. Alternatively, when there is no pendingdata which can be used for transmission after the last transmissionwithin the corresponding SC period, all triggered D2D BSRs should becancelled. At this time, a cancel procedure is performed after the lasttransmission within the corresponding SC period. Alternatively, sinceall pending data which can be used in the buffer for transmission of theremaining D2D grant(s) for the corresponding SC period can be accepted,if the triggered D2D BSRs are cancelled before the corresponding SCperiod, the D2D BSRs are triggered within the SC period and the datareaches the buffer after the D2D BSRs are cancelled.

Further, in the current system, all D2D BSRs transmitted during atransmission time interval (TTI) always reflect the buffer state afterall MAC PDUs are constructed during the TTI. In such a scheme, when theD2D BSRs are transmitted before the last data transmission within the SCperiod, the D2D BSRs may report data for which the grant has beenalready received and, as a result, the eNB may allocate resources largerthan required, which nay result in wasting resources.

Accordingly, the present disclosure proposes the following D2D BSRtriggering method to overcome the problems.

The D2D BSR transmitted in the TTI reflects the buffer state inconsideration of all MAC PDUs constructed during the corresponding TTIand also MAC PDUs that can be constructed using the remaining D2Dgrant(s) valid during the corresponding SC period in which the D2D BSRsare transmitted. Alternatively, the D2D BSRs are transmitted after thelast data transmission within the SC period. Alternatively, whenreceiving the D2D BSRs from the UE, the eNB calculates a buffer size inthe HE based on equation (1) below.

Buffer size=size of buffer received from UE in D2D−BSR remaining grantsavailable within SC period in D2D grants allocated to UE after TTI inwhich D2D BSRs are received   (1)

FIG. 11 schematically illustrates a D2D link quality measurement methodfor a UE according to the present disclosure. FIG. 11 illustrates anexample in which a PHY layer first measures RSRP/RSRQ/RSSI for discoveryresources and decodes discovered PDUs in each discovery resource.

Referring to FIG. 11, in step 1, with respect each of discoveryresources R1 to R6 within a separated RX pool for discovering a relay(or PS), the PRY layer measures RSRP/RSRQ/RSSI for discovery resourcesthat carry DMRSs. In step 2, the PHY layer decodes discovered PDUs ineach discovery resource and, when the decoding is successful (whenpassing through the CRC), maintains a measurement result of thecorresponding PDUs and filter the measurement result of the same UE IDaccording to steps 3 to 5. Otherwise, the PHY layer removes or discardsthe measurement result. FIG. 11 illustrates an example in which PDUs 1,3, 5, and 6 are successfully decoded and corresponding measurementresults M1, 3, 5, and 6 are maintained.

In step 3, the determines whether a discovery message within the decodeddiscovery PDUs is a relay UE discovery message and, when the discoverymessage is the relay UE discovery message, maintains the measurementresult and proceeds to step 4. Otherwise, the UE removes or discards themeasurement result. FIG. 11 illustrates a case where MSG 1, 3, and 6 arediscovery messages and, accordingly, corresponding measurement resultsM1, 3, and 6 are maintained.

In step 4, the UE determines a UE ID of the relay UE having transmittedthe corresponding discovery message. At this time, the measurementresult corresponding to the discovery message is a measurement resultfor a link with the relay UE identified by the determined UE ID.

In step 5, the UE filters RSRP/RSRQ/RSSI for the measurement results ofthe same UE

FIG. 12 schematically illustrates another D2D link quality measurementmethod for a UE according to the present disclosure. FIG. 12 illustratesan example in which the PHY layer measures RSRP/RSRQ/RSSI for discoveryresources after decoding discovered PDUs in each discovery resource.

Referring to FIG. 12, in step 1, the PHY layer monitors discoveryresources included in one or more discovery RX pools and decodes thediscovered PDUs in each discovery resource of the discovery RX pool. ThePHY layer monitors each of discovery resources R1 to R6 within aseparated RX pool for discovering the relay (or PS) and decodes thediscovered PDUs in each discovery resource of the discovery RX pool.FIG. 12 illustrates a case where PDUs 1, 3, 5, and 6 are discovered anddecoded in RI, 3, 5 and 6, respectively.

In step 2, the PITY layer measures RSRP/RSRQ/RSSI for resource elementsthat carry DMRSs in discovery resources corresponding to thesuccessfully decoded. PDUs (having passed through the CRS). Further,according to steps 3 to 5, filtering is performed on the measurementresult of the same UE ID. FIG. 12 illustrates a case in whichRSRP/RSRQ/RSSI for PDUs 1, 3, 5 and 6 are measured (M1, 3, 5,and 6).

In step 3, the UE determines whether a discovery message within thedecoded discovery PDUs is a relay UE discovery message and, when thediscovery message is the relay UE discovery message, maintains themeasurement result and proceeds to step 4. Otherwise, the UE removes ordiscards the measurement result. FIG. 12 illustrates a case where MSG 1,3, and 6 are discovery messages and, accordingly, correspondingmeasurement results M1, 3, and 6 are maintained.

In step 4, the LIE determines a UE ID of the relay UE having transmittedthe corresponding discovery message. At this time, the measurementresult corresponding to the discovery message is a measurement resultfor a link with the relay UE identified by the determined UE ID.

In step 5, the UE filters RSRP/RSRQ/RSSI for the measurement results ofthe same UE ID.

In another method of selecting/re-selecting the relay UE, an AS layermay transmit each of the received discovery messages to a higher layer(that is, ProSe protocol) along with a corresponding PC5 link qualitymeasurement value. The ProSe protocol analyzes each relay UE discoverymessage received by a lower layer, generates a final candidate list ofthe relay UEs that meet a reference of the higher layer, and performs amoving average (PC5 signal strength filtering) to avoid a suddenwireless change for the relay UEs in the final candidate list. The ProSeprotocol ranks relay UEs having a signal strength higher than a (pre)setthreshold value in a descending order of the signal strength and selectsa best relay UE. The ProSe protocol accesses the corresponding relay UEby using PC5 signaling protocol messages. According to an embodiment,the ranking may be performed only when two or more relay UEs exist.

In another method of selecting/re-selecting the relay UE, the ProSeprotocol analyzes each relay UE discovery message received by the lowerlayer, generates the final candidate list that meets the reference ofthe higher layer, provides the generated final candidate list to the AS,and then receives a selected relay UE from the AS. Further, the ProSeprotocol accesses the selected relay UE by using PC5 signaling protocolmessages. The AS layer performs moving average (PC5 signal strengthfiltering) to avoid a sudden wireless change for the relay UEs in thefinal candidate list received from the ProSe protocol, and ranks therelay UEs having a signal strength higher than a (pre)set thresholdvalue in a descending order of the signal strength and selects a bestrelay UE. According to an embodiment, the ranking may be performed onlywhen two or more relay UEs exist. The AS informs the higher layer (ProSeprotocol) of the selected relay UE.

Meanwhile, the UE identifies the measurement corresponding to the relayID and then filters measurement values corresponding to the same relayID. However, due to collision, the discovery PDUs may not besuccessfully received within predetermined discovery periods and,particularly, a measurement result for a particular relay ID may be notperiodically received. For example, as illustrated in FIG. 13, whenmeasurement values M1 to M5 should be received according to apredetermined measurement window, if the measurement values M2, M3, andM4 are not received, an average of M1 and MS provides an inaccurateresult. According to the present disclosure, in this case, when the lastmeasurement result corresponds to a measurement window x and a newmeasurement result corresponds to a measurement window Y, ifY−X>threshold value, the UE processes the new measurement valuecorresponding to the measurement window Y as an initial measurementvalue and ignores or discards previous measurement values of themeasurement window X. The threshold value may be pre-defined or presetby the network. Further, instead of measurement window numbering, asystem time which is measured by the AS or corresponds to a time atwhich the measurement is received may be used.

According to another embodiment, when the measurement value is notreceived in the measurement window X, a measurement value of ameasurement window X−1 may be used as the measurement value of themeasurement window X. Such a method may be applied only when themeasurement is not omitted in N successive measurement windows. N may bepre-defined or preset by the network.

According to another embodiment, in order to avoid omission andcollision of the measurement result, the relay UE may always make arequest for relay UE discovery resources to a serving eNB. The servingeNB may allocate resources dedicated for the discovery.

According to the relay UE search/discovery method of FIGS. 2 to 13described above, the subject that determines whether to perform thesearch/discovery may be the remote UE or the relay UE and theRSRP/RSRQ/RSSI used for determining whether to perform thesearch/discovery may be for the link between the remote UE and the relayUE or the link between the relay UE and the network. Further, thedrawings and embodiments described above may be individually used or acombination of two or more thereof may be used.

FIG. 14 illustrates a configuration of a UE according to an embodimentof the present disclosure. The UE of FIG. 14 may be a remote UE or arelay UE.

A UE 1400 may include a transceiver 1410 for performing datacommunication with various network nodes and an eNB and a controller1420 for controlling the transceiver 1410. In the specification, alloperations of the remote UE or the relay UE may be construed as beingperformed by a control of the controller 1420.

Meanwhile, although FIG. 14 illustrates the transceiver 1410 and thecontroller 1420 as separate elements, the transceiver 1410 and thecontroller 1420 may be implemented as one element.

The above described operations may be implemented by providing a memorydevice storing a corresponding program code to the entity of thecommunication system, the function, the base station, the load manager,or a specific structural element of the terminal. That is, the entity,the function, the load manager, or the controller of the terminalcarries out the above described operations by reading and executing theprogram code stored in the memory device by means of a processor or aCPU.

The entity, the function, the base station, the load manager, variousstructural elements of the terminal, modules and the like may beoperated by using a hardware circuit, e.g, a complementary metal oxidesemiconductor based logic circuit, firmware, software, and/or acombination of hardware and the firmware and/or software embedded in amachine readable medium. As an example, various electrical structuresand methods may be carried out using electrical circuits such astransistors, logic gates, and application specific integrated circuits(ASICs).

While the present disclosure has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the scope of the present disclosure. Therefore,the scope of the present disclosure should not be defined as beinglimited to the embodiments, but should be defined by the appended claimsand equivalents thereof.

What is claimed is:
 1. A method of device to device directcommunication, the method comprising: receiving, by a user equipment(UE), one or more discovery messages on a discovery channel from one ormore candidate relay UEs; measuring power of reference signalsassociated with the discovery channel on which each discovery message isreceived; filtering, by the UE, power measurements corresponding to asame relay UE ID among power measurements corresponding to the one ormore discovery messages; and selecting a relay UE among the one or morecandidate relay UEs based on the filtered power measurements.
 2. Themethod of claim 1 wherein the discovery message is a discoveryannouncement message.
 3. The method of claim 1, wherein decoding the oneor more discovery messages for cyclic redundancy check (CRC) andgenerating the power measurements are performed by a physical layerwithin the UE, and wherein filtering the power measurements is performedby a radio resource control (RRC) layer within the UE.
 4. The method ofclaim 3, wherein the physical layer generates the power measurementsbased on a measurement instruction from the RRC layer.
 5. The method ofclaim 1, further comprising: identifying, from a discovery message ofthe one or more discovery messages, a relay UE ID of a candidate relayUE that transmits the discovery message.
 6. The method of claim 5,wherein identifying the relay UE ID of the relay UE is performed by ahigher layer within the UE, and the identified relay UE ID of the relayUE is transferred by the higher layer to a radio resource control (RRC)layer within the UE.
 7. The method of claim 6, wherein the higher layercomprises a medium access control (MAC) layer and a proximity service(ProSe) protocol layer.
 8. The method of claim 7, wherein the MAC layertransmits the discovery message and the power measurements to the ProSeprotocol layer.
 9. The method of claim 1, wherein a proximity service(ProSe) protocol layer determines that e discovery message is adiscovery announcement message.
 10. A user equipment (UE) apparatus fordevice to device direct communication, the UE apparatus comprising: atransceiver configured to: transmit and receive signals for a device todevice direct communication; and a controller configured to: receive oneor more discovery messages on a discovery channel from one or morecandidate relay UEs, measure power of reference signals associated withthe discovery channel on which each discovery message is received,filter power measurements corresponding to a same relay UE ID amongpower measurements corresponding to the one or more discovery messages;and select a relay UE among the one or more candidate relay UEs based onthe filtered power measurements.
 11. The UE apparatus of claim 10,wherein the discovery message is a discovery announcement message. 12.The UE apparatus of claim 10, wherein the controller is furtherconfigured to include a physical layer and a radio resource control(RRC) layer, wherein the physical layer receives and decodes the one ormore discovery messages for cyclic redundancy check (CRC) and generatesthe power measurements, and wherein the RRC layer filters the powermeasurements.
 13. The UE apparatus of claim 12, wherein the physicallayer generates the power measurements based on a measurementinstruction from the RRC layer.
 14. The UE apparatus of claim 10,wherein the controller is further configured to: identify, from adiscovery message of the one or more discovery messages, a relay UE IDof a candidate relay UE that transmits the discovery message.
 15. The UEapparatus of claim 10, wherein the controller is further configured toinclude a higher layer and a radio resource control (RRC) layer, andwherein the higher layer identifies the relay UE ID of the relay UE andtransfers the identified relay UE ID of the relay UE to the RRC layer.16. The UE apparatus of claim 15, wherein the higher layer comprises amedium access control (MAC) layer and a proximity service (ProSe)protocol layer.
 17. The UE apparatus of claim 16, wherein the MAC layertransmits the discovery message and the power measurements to the ProSeprotocol layer.
 18. The UE apparatus of claim 10, wherein a proximityservice (ProSe) protocol layer determines that the discovery message isa discovery announcement message.